A number of factors influence the trajectory of a golf ball which has been struck by a golf club. These factors include, for example, the golfer's stance, the golfer's swing and the design of the golf club. Many golfers spend a considerable amount of time and money to develop a stance and swing that will allow the golfer to strike a golf ball effectively to project a ball along an optimum trajectory. Despite these efforts, many golfers have difficulty mastering control over their swing and the ball trajectory and consequently seek to improve their game by selecting golf clubs which are designed to provide superior performance and playability. As used herein, the terms "performance" and "playability" refer to the ease with which a golf club can be used to produce consistently satisfactory results.
Golf clubs are generally divided into three main categories: putters, irons, and woods. The golf clubs in the woods category include the driver, which is also known as the number one wood, and the fairway woods, which typically include the number three, four, five, and seven woods. Most of the club heads in the woods category are currently fashioned from metals such as titanium, and such heads commonly have a hollow, thin-walled design. The performance and playability of a driver is particularly important, because the driver is customarily used in making the longest shot a golfer takes when playing a given hole. Thus, an error made when striking a golf ball with a driver will have particularly adverse affect on the trajectory of the golf ball.
It is known in the art that certain parameters relating to the design of a driver head will influence the performance and playability of the driver. For example, placing most of the weight of a head about its exterior edges will increase the mass moment of inertia of the head, and the head will consequently tend to provide a straighter ball trajectory even when the ball strikes the club face at a less than optimal point.
Another parameter which influences the playability of a driver is the position of the center-of-gravity of the head. U.S. Pat. No. 5,050,879 to Sun and U.S. Pat. No. 5,013,041 to Sun disclose driver heads having cavities which are adapted to receive various sized weights so as to adjust the center-of-gravity of the head and customize the driver head to best suit a particular golfer. U.S. Pat. No. 4,461,481 to Sunyong, and U.S. Pat. No. 3,951,413 to Bilyeus disclose drivers with heads having a center-of-gravity that is repositioned while the club is swinging. The heads disclosed in these patents achieve this effect by the placement of moveable weights within the head. U.S. Pat. No. 4,432,549 to Zebelan discloses a driver head which controls the position of the center-of-gravity by varying the wall thicknesses of the various sides of the head.
Other parameters which can influence the playability of a driver include the aerodynamic characteristics of the head, as disclosed in U.S. Pat. No. 4,444,392 to Duclos, and the angular orientation of the club face which is used to strike a golf ball. In U.S. Pat. No. 5,366,223 to Werner, a driver head is disclosed that has a face which is tilted upward at an angle of 20 degrees or more at the toe to cause a better correlation between a typical golfer's hit pattern and the perimeter of the club face. It is also known that by maximizing the dynamic face angle of a driver head, an average golfer will be better able to close the face angle at the moment of impact of the driver head and the golf ball. The dynamic face angle is measured between the line extending from the hosel (i.e., the point at which the shaft is attached to the head) to the center of gravity of the head, and the line which is tangent to the outermost point of the front surface of the head. The face angle is measured between the line along which the head is moving at the moment of impact with a golf ball and the horizontal axis of the elliptical front surface the head, and is "closed" when the line of movement is substantially normal to the horizontal axis.
From the foregoing, it will be understood that a variety of parameters relating to the design of a driver head can impact the performance and playability of the club on which it is used. It will also be understood that a need exists for a driver head in which multiple parameters are defined in a specific way, such that their combined effect is to produce a driver having greatly enhanced performance and playability.